Most days, Ed Murtagh spends hours behind his desk in Suite 1028 of the south building at the U.S. Department of Agriculture, trying to figure out how to conserve energy, reduce waste and make other environmental improvements.

But starting this month, Murtagh will regularly get up from his desk, walk outside and literally make the department greener.

Murtagh is among 80 volunteers at the USDA who are lending their sweat and muscle to an organic garden created by Agriculture Secretary Tom Vilsack along the Mall, on the grounds of the agency's headquarters at 14th Street and Independence Avenue SW.

Vilsack carved out the garden last year from an asphalt parking lot. He grabbed a jackhammer and challenged USDA facilities across the country to follow suit and create what he calls a People's Garden.

As of last week, 255 gardens have been established by Agriculture Department workers worldwide, including an indoor lettuce garden in North Carolina and a vegetable garden on the grounds of the U.S. Embassy in South Korea. All of the food grown at these gardens -- 29,656 pounds last year -- is donated to food pantries and soup kitchens. The garden at USDA headquarters last year yielded more than 300 pounds of peas, peppers, tomatoes, eggplants and other produce, which was given to D.C. Central Kitchen.

During its debut, the garden was tended by the Agriculture Department's landscape firm, two college interns and an ad hoc group of USDA employees.

This year, the agency decided it would require volunteers to complete a six-week Master Gardener training program and pass an exam before being allowed to volunteer. Taught by extension-service experts who flew to Washington from throughout the country, the course covered topics including botany and storm-water management. That requirement did not dampen enthusiasm for the program. The class's 80 spaces were filled within 15 minutes of the announcement, and 70 other people were turned away, said Livia Marques, director of the People's Garden Initiative.

"People like to pick on government employees," Marques said, adding that during the planning of the initiative some officials expressed doubts about whether the agency could persuade workers to volunteer. "So many people want to be involved in this," she said. "It's wonderful."

Marques said the garden serves as a living exhibit for the 25 million annual visitors to the Mall, many of whom stop and ask questions of the gardeners and learn about sustainable agricultural practices.

"We get people who don't recognize a tomato plant, to people who tell us what we should be doing," Marques said. "That's the best part -- the way the public interacts with this garden."

In addition, every Friday during the growing season, the Agriculture Department holds public events at the garden, with guests including chefs talking about how to cook with the vegetables grown there and experts discussing such topics as using a rain barrel in a home garden.

"It's a really good way to connect what we do every day at USDA with the average American," said Julie Grogan Brown, an Agriculture Department worker who is part of the volunteer program.

The gardeners are also ripping out invasive species on the department's grounds and replacing them with native grasses, plants and trees. They also plan to pair complementary plants, such as tomatoes and basil, that help one another flourish. Vegetables are grown in raised beds filled with organic soil and compost.

The agency is considering installing a beehive on its roof, to supply bees that will pollinate the plants, as well as a "bee-cam" so the public can learn about bee activity. And it is managing storm-water runoff from a nearby parking lot by creating a rain garden of wetland plants that will absorb the water and prevent it from running into storm drains bound for the Chesapeake Bay.

The Agriculture Department team has faced several challenges in creating the garden. The Metro runs directly underneath, limiting the amount of digging that can take place. And the Mall, which was originally a swamp that was topped with fill, is not exactly the best quality for agricultural purposes. To add nutrients, the gardeners are growing crimson clover and rye. And because the USDA is on the Mall, changes to the exterior, including the garden, must be approved by the U.S. Commission of Fine Arts and the National Capital Planning Commission. Even the location of a beehive had to be carefully evaluated.

"We couldn't put it in the garden because of liability," Marques said. "So it will go on the roof, at a safe distance."